CHAPTER 9
Chemical Quantities
9.1


-The equation for a chemical reaction
indicates the relative numbers of reactant
and product molecules required for the
reaction to take place. Using the equation
permits us to determine the amounts of
reactants needed to give a certain amount
of product or to predict how much product
we can make from a given quantity of
reactants.
a. For example a box of cake mix gives
ingredients and instructions to make a certain
amount of cake batter.
9.1 (continued)
 Now
we can use an equation to predict
moles
 The moles of products can be predicted
by the given number of moles of
reactants will yield.
 For example: The decomposition of 2 mol
of water = 2H2O – 2H2 + O2
 This tells us that the water yields 2 mol of
H2 and 1 mol of O2.
9.1: More Practice
 How
much is yielded from the
decomposition of 4 mol of water?
 4 mol of H2 and 2 mol of O2
 Since the total value was just multiplied by
2, we multiply the reactants by 2 as well.
9.1: Using Mole Ratios
 If
the number isn’t easily exchangeable,
as 2 and 4 are, then we have to balance
the equation first.
 For example: What if 5.8 mol of water is
decomposed?
- First we balance the equation by
dividing by two, resulting in H2O – H2 + ½ O2
- Then multiply each by 5.8, resulting in
5.8H2O – 5.8H2 + 2.9O2.
9.2
 Section
is talking about balancing
equations by getting the same weights.
You change the coefficients.
 You multiply the mass in grams X the value
of one mole of that element or substance
over the molar mass of the substance in
grams
9.2 continued






1. balance the equation for the reaction
2. convert the masses of reactants of
products to moles
3. use the balanced equation to set up the
appropriate mole reactions
4. use mole ratio(s) to calculate the number
of moles of the desired reactant or product
5. convert back to mass
Example:
9.2. continued
 Stoichiometry-
the process of using a
balanced chemical equation to
determine the relative masses of
reactants and products involved in a
reaction
9.2 continued
 When
you compare two reactions, they
need to be balanced, and you would be
comparing how much of a same
substance they will react with.
 Example: two antacids: baking soda and
milk of magnesia both consume stomach
acid, but in order to find out which
consumes more, you need to find how
many moles of stomach acid reacts with
a gram of each.
9.2 practice
 We
need to know how much carbon
dioxide 1.00x10^3 lithium hydroxide can
absorb. The products are water and
lithium carbonate
 The equation would be:
LiOH(s) + CO2(g) → Li2CO3(s) + H2O(l)
 What is the balanced equation?
More practice
 2LiOH(s)
 Convert
+ CO2(g) → Li2CO3(s) + H20(l)
the given mass of LiOH into moles
using the molar mass: 23.95g
 41.8 mol
 The
L
mole ration is 1 mol CO2
2 mol LiOH
 Thus
calculate the moles of CO2
 20.9
mol CO2
 Calculate
the mass of CO2 using its molar
mass: 44.01 g
 920g.
 Therefore,
1.00x10^3 g of LiOH(s) can
absorb 920 g of CO2(g)
9.3 Limiting Reactants and
Percent Yield
 Limiting
Reactant- The reactant in a
chemical reaction that limits the amount
of product that can be formed.
9.3 The Concept of limiting
reactants
 If
you are making a chain reaction, you
need to form a ratio with all of the
reactants.
 All ingredients must be used in the correct
ratio
9.3 (continued)
 The
reactant that runs out first is the
limiting reactant. You can not continue to
produce that product with an item after it
has run out.
9.3 Practice
2
slices of bread + 3 pieces of meat + 1
slice of cheese = 1 sandwich
 To make 10 sandwiches, you would have
to multiply 10 to each of the ingredients.
 2(10) + 3(10) + 1(10) = 10 sandwiches
 20 slices of bread, 30 pieces of meat, and
10 slices of cheese will make 10
sandwiches.
9.3 More Practice
2
slices of bread + 3 pieces of meat + 1
slice of cheese = 1 sandwich
How much of each item would I
need to make 40 sandwiches
for the football team at their
upcoming game?